Mechanoluminescence excitation in alkali halide crystals and colouration decay in microcrystalline powders

The mechanoluminescence (ML) of NaCl, NaBr, NaF, LiCl and LiF crystals ceases at 105, 58, 170, 151 and 175°C respectively. Both the temperatureT _c at whichML disappears and the temperatureT _s required to induce a particular percentage of colouration decay in a given time, decreases with increasing nearest neighbour distance in alkali halide crystals. This perhaps suggests that similar processes cause the disappearance ofml in alkali halide crystals and the colouration decay in their microcrystalline powders. It is shown that mobile dislocations may cause the leakage of surface charge and the decay of colouration in microcrystalline powders.     

Reflectance spectra and thermoluminescence of NaF coloured in an electrodeless discharge

A comparative study ofγ-ray colouration and electrodeless discharge excitation is reported for NaF. New absorption bands and glow peaks were found. These are shown to be characteristic of electrodeless discharge method of colouration. These are attributed to the multiple types of defects. Further, it is shown that the process by which such defects are formed is strongly temperature dependant. A tentative explanation for the peculiar characteristic of the electrodeless discharge excitation is put forth. The possibility of exploiting these peculiarities for the study of certain properties of colour centres is pointed out.     

Reflectance spectra and thermoluminescence of alkali halides coloured in an electrodeless discharge

Microcrystalline powders of NaCl, KCl and KBr are coloured in electrodeless discharge. Reflectance and TL studies of these coloured powders are reported. It is concluded that colouration of powders can be understood by considering them as an admixture of perfect and imperfect lattices, and differs from that of single crystals. It is suggested that some of the descrepancies reported on TL data may be due to such a difference. Further, it is shown that a better correlation can be had if TL data are presented along with the corresponding optical measurements. Adoption of such a procedure may help to remove the descrepancy in TL data.     

Isothermal decay of colour centres in microcrystalline powders of alkali bromides

The bleaching of F-centres on storing in darkness of electrolytically coloured single crystals and microcrystalline powders of solid solutions of KBr with other alkali bromides is reported. The colouration of the microcrystalline powders decays isothermally while that of single crystals is comparatively stable. The decay proceeds slower in the powders of mixed crystals than in the pure materials. A tentative explanation is suggested.     

Effect of electrolytic colouration on dislocation density in KBr and KCl

Average dislocation density in a number of electrolytically coloured and uncoloured crystals of KBr and KCl has been measured using the etch-pit technique. A decrease in density of dislocation after electrolytic colouration has been observed. This is attributed to the change in the dislocation pattern inside the crystals during colouration to produce more number of vacancies under the typical conditions of large electric field gradient at high temperature.     

A comparison of thermo- and photo-chromic behaviour in films of amorphous WO3

Amorphous films of WO₃ have been prepared by sublimation in a partiaal pressure of oxygen, and then coloured by either heat-treatment or U.V. radiation. Thermo-chromic films are extremely stable with respect to oxygen and have been compared with oxygen deficient crystals of WO₃. Photo-chromic films are extremely unstable in an oxygen environment similar to hydrogen tungsten bronzes. The variation of the thermoelectric power with colouration suggests that the density-of-states in the neighbourhood of the Fermi energy differs in films coloured by the two methods.     

Lyoluminescence mechanism of gamma and additively coloured alkali halides in pure water

The light emitted on dissolution of gamma and additively coloured crystals of NaCl, NaBr, KCl, KBr, CsCl and CsBr in pure water is studied. Experiments on gamma irradiated crystals have proved that the light emission originates from the recombination of released F-centres with trapped holes (V₂-centres) at the water-solid interface. Exceptionally pure additively coloured crystals having only F-centres produced no light when dissolved in pure water. However, relatively impure crystals emit light on dissolution due to the recombination of F-centres with traces of impurity ion centres in these crystals.     

On the colloidal absorption bands in rubidium chloride and rubidium bromide crystals coloured with sodium

Colloidal absorption bands in rubidium chloride and rubidium bromide crystals coloured with sodium have been investigated. After a certain heat treatment of the RbCl and RbBr crystals containing F-centers, colloidal bands were observed at 585 mμ for RbCl and at 600 mμ for RbBr. The measured positions of these bands were compared with those calculated by means of the theory ofDoyle. Measurements of the areas of the absorption curves were also carried out at different temperatures.     

Measurement of electron energy and density in an H. F. electrodeless ring discharge

The electron temperatureT _e and the electron density were measured as functions of the radial distance in a 10 Mc/s electrodeless ring discharge in hydrogen in the pressure range 0.1–0.3 Torr. It was found thatT _e remains nearly constant along the radius of the cylindrical vessel. The measured values ofT _e have been compared with those observed by other workers and an estimate of the effective electric field in the discharge has been made. From this estimate it has been inferred that even after the first stage of the ring discharge is well established the longitudinal component of the electric field remains of considerable importance. The radial density distribution of the electrons was found to be different from those in an uniform electric field. This deviation in the radial density distribution has been attributed to the influence of the azimuthal electric field.     

Emission und Schwingungsverteilung der 1. neg. Gruppe und der 2. pos. Gruppe in einem Stickstoffplasma

The intensity of the first negative system ofN ₂ ⁺ (B ² Σ _u ⁺ -X ² Σ _g ⁺ and of the second positive system ofN ₂(C ³ Π _u -B ³ Π _g ) was observed in the discharge and in the afterglow as function of discharge current. An a. c. discharge in pure nitrogen was used at pressures of about 5 torr. The intensity of the first negative system ofN ₂ ⁺ — in the discharge and in the afterglow — rises to a maximum and decreases with further increase of the discharge current. The afterglow intensity of the second positive system ofN ₂ shows a maximum too. In the discharge, however, the intensity of the second positive system ofN ₂ increases with increasing discharge current. The relative population of the vibrational levelsN _v′ =i/N _v′ =0 (i=1,2,3,4) of theB ² Σ _u ⁺ state ofN ₂ ⁺ , in the discharge and in the afterglow, increases with increasing discharge current, while the relative population of the vibrational levelsN _v′ =i/N _v′ =0 (i=1, 2, 3, 4) of theC ³ Π _u state ofN ₂ reaches a maximum in the discharge. There seems to be evidence that the first negative system ofN ₂ ⁺ is not excited by electron impact withN ₂ molecules in ground state under the discharge conditions in question.     

Untersuchung über die gasionisierende Strahlung einer Entladung II

This paper gives a report on measurements of the coefficient of absorption and intensities of a gas-ionizing radiation, which is emitted by a gas discharge. Earlier measurements in oxygen with a discharge in a cylindrical electrical field had yielded components of radiation with values ofμ≈550,μ≈250, andμ= 38 cm^?1 according to 760 mm Hg. By new measurements using a spark discharge an additional component with a value ofμ=2,5 has been found, which already has been measured by other authors. Measurements with mixtures of oxygen and nitrogen are compared with results of measurements in air. From this it may be deduced that the gas-ionizing radiation effective in air is essentially emitted by nitrogen and ionizes oxygen, the coefficient of absorption being aboutμ≈5 cm^?1. The number of ionizing quantums emitted per ionizing collision of electrons in the discharge tube is about 10^?3 for oxygen, nitrogen, and air. In oxygen this figure proves to be essentially independent ofE/p. In air, however, this figure is reduced with increasing values ofE/p. The absorption of the ionizing radiation in air is increased by the addition of methane (μ=960 cm^?1 for 760 mm Hg of methane). In carbon dioxyde several components of ionizing radiation are found, with coefficients of absorption in the range 200<μ<800.     

Colour centres in powdered KI

Fine powder of KI was coloured in an electrodeless discharge. Due to quick bleaching of the F centres produced in this method, it was possible to prepare the samples that were almost free from the F centres. High concentration of the electron deficient centres could be produced, which were studied by measuring the diffused reflectance. A band at 354 nm is shown to be composed of two overlapping bands. Further, growth of a band appearing at 265 nm is studied. Bleaching characteristics of the samples are studied and it is shown that, similar to F centre bleaching, bleaching of these samples also proceeds in at least two steps. The difference between two components of the bleaching curves is quite marked. Further it is showed that the components are related to the presence of different absorption bands and appear at different stages of colouration.     

Lyoluminescence mechanism of additively and gamma coloured alkali halides in fluorescent and chemiluminescent solutions

Lyoluminescence of gamma irradiated and additively coloured NaCl, NaBr, KCl and KBr crystals when dissolved in fluorescent and chemiluminescent aqueous solutions is investigated. Spectral analysis of the emitted light has shown that lyoluminescence spectra are similar to the fluorescence spectra of these solutions. Luminescence takes place when a fluorescent acceptor is directly excited by a liberated F-centre (hydrated electron e^-_aq) or indirectly by an energy transfer from a released excited halide ion ∥X^-∥¹ (solvated hole after recombination with hydrated electron). Oxygen, in general, has a marked quenching effect on luminescence. In chemiluminescent systems, its presence is essential to provoke luminescence in a sequence of events leading to a fluorescent end product.     

Sättigungsverhalten und Verlauf der Elektronentemperatur beim Argon-Ionenlaser

Recently saturation of laser power ofCW ion lasers has been observed with large bored laser tubes made of metal segments. The saturation was observed in Argon, Krypton and Xenon in high current regions. In this case it was necessary to calculate the correlation between the electron temperature, electron- and ion-density and on the other hand the discharge quantities as current density and voltage drop. By measuring the discharge quantities at optimum laser power it is possible to determine the optimum electron temperature for any current density. The comparison of the run of these quantities leads to the assumption that the saturation mechanism causes a decrease of the optimum electron temperature.     

Rotational motion of F− off-center defects in NaBr

The correlation time τ of the rotational motion of dilute F^? off-center defects in NaBr single crystals was studied by nuclear spin relaxation between 1.4 and 70 K. Above 15 K, the motion was found to be thermally activated with an activation energy of 110 K. Below 15 K, a deviation from the Arrhenius behavior was observed, which results in a linear relation τ ∝ 1/T for T < 8 K. The data were interpreted in the framework of phonon-assisted tunneling models.     

Levels in182W populated in the decay of182Ta

Theγ-rays emitted in theβ-decay of¹⁸²Ta have been reinvestigated with improved statistics in attempting to clarify the reported new levels at 1460.41, 1592.98, 1620.36, 1712.29 and 1762.91 keV in¹⁸²W observed in theβ-decay of¹⁸²Ta. The present study demonstrated that the fifteen newγ-rays, which were used to support the existence of the five new levels, are not relevant to theγ-decay of¹⁸²Ta. Therefore the five new levels are not populated in this decay. Additionally, theγ-ray with an energy of 1035.6 keV (0 ₂ ⁺ →2 ₁ ⁺ ) deexciting theβ-band head in¹⁸²W is observed for the first time in the present decay study and the previous tentative placement of the 351.0 keVγ-ray in the level scheme is confirmed by the present coincidence measurements.     

Mechanoluminescence characterisation of γ-irradiated (KNa)Br:Ce3+ phosphor

The mechanoluminescence (ML) of γ-irradiated coloured powder of (KNa)Br:Ce(0.1–10 mol%) phosphor is reported in this paper. The samples are prepared by wet chemical method. The ML intensities are found to be dependent on concentrations of Ce³⁺ ion and γ-rays radiation dose. The variation of peak ML intensity of (KNa)Br:Ce(0.5 mol%) with different γ-rays dose is found as linear up to 2.5 kGy high dose from 0.08 kGy, whereas for the KBr:Ce(0.5 mol%) and NaBr:Ce(0.5 mol%) samples the ML intensities increases sublinearly. The prepared sample shows minimum fading in ML intensity. The ML characterisation shows the good linearity, less fading and simple ML glow curve structure, thus the prepared material may be useful for radiation dosimetry.     

Influence of halogenides on luminescence from silver molecular clusters in photothermorefractive glasses

It is shown experimentally that a rise in the sodium halogenide (NaCl, NaBr) concentration in photothermorefractive glasses increases the intensity of luminescence from silver neutral molecular clusters. Substitution of NaBr for NaCl with their concentration being the same shifts the luminescence band toward longer waves and raises its intensity. These findings can be explained by the formation of molecular clusters of type Ag _n -Hal (Hal = Cl, Br) in photothermorefractive glass.     

Bandcrossing inK≠0 bands

It is shown that in the crossing of two bands withK≠0 in deformed nuclei, two new effects are observed that are not seen in the crossing ofK=0 bands; namely, a)I _critical at which the bands cross is lowered and b) Band crossing occurs at different values ofI _crit for oddI (orI+1/2 in oddA) and evenI (orI+1/2). These predictions are shown to be observed in the odd-A rare-earth nuclei where data are available to high spin.     

Measurement of thomson and rayleigh scattering in a preionizationZ-pinch

A 90° scattering experiment with a preionizationZ-pinch is described. The first part describes conventional measurements of the electron temperature and density (Thomson scattering). In the second part of the experiment Rayleigh scattering from excited hydrogen atoms was observed during very early phases of the discharge. This observation is possible because the Rayleigh scattering cross section of hydrogen atoms in the second and third quantum states is very large because of the small difference in the energy of the photons ofH _α (6563 Å) and the light of a ruby laser (6943 Å). Spectral resolution of this part of the scattered light yields a minimum value for the ion temperature.